1. Field of the Invention
This invention relates to a powder detergent composition. More particularly, this invention relates to a powder detergent composition which has a high whiteness without coloration in the powder state and which can blue an article during the washing treatment thereof thereby to attain a highly improved whitening effect.
2. Description of the Prior Art
It is well known in the detergent art that a whitening effect can be attained by incorporating in fabric-washing detergent compositions a so-called bluing agent and dyeing the washed article with a faint blue color (a so-called bluing treatment). The color tone of these bluing agents for imparting the whitening effect to washed articles is not a pure blue, but rather is of a slightly reddish violet color. Therefore, if such a bluing agent is directly blended in a powder detergent, the detergent is slightly colored red because of the inherent color property of the bluing agent, and the desired pure white color and fresh appearance of the detergent are drastically lowered. In order to avoid this undesired coloration phenomenon, it is necessary to coat the bluing agent or the like so that its color is masked or concealed.
Further, the whitening effect of the bluing agent can result in a reduction of the whiteness if an excessive amount thereof is used, and such undesired phenomena as spot dyeing of fibers owing to uneven application of the detergent can occur. In order to prevent occurrence of such undesired phenomena, the absorbability (absorption) of the dye is generally controlled by various means. This control treatment in turn causes the problem that not all of the added dye is effectively utilized and, in extreme cases, the majority of the dye is not absorbed by the fibers, but rather is discharged together with waste water, as occurs with pigment-type bluing agents. Still further, even though the amount of dye absorption is controlled with currently available bluing agents, because the principal purpose of using bluing agents is to overcome yellowing of clothes by using a dye of a complementary color, when washing is repeated over a long period, reduction of the color clarity or whiteness of the fabrics cannot be avoided. Moreover, for some bluing agents, because of the inherent properties of the dye or the method of compounding it in the detergent composition, the dye is decomposed during storage of the powder detergent and it fails to exhibit its intended activity, or the dye when dissolved in water is scarcely absorbed in the fibers but rather adheres to the tank of the washing machine to make it dirty.